Preheat oven 400 degrees.

In a saucepan bring the heavy cream to a boil. Reduce heat and allow it to simmer for 8 minutes. Stir occasionally and do not let it boil over.

Add 1 1/2 cups Gruyere cheese to cream. Stir until the cheese is fully melted and becomes a sauce.

Spray an 11x7 baking pan with cooking spray. Place a layer of sweet potatoes at the bottom of the dish, followed by about 1/4 cup of sauce. Repeat the layers until you end with sauce. Then top with the remaining 1/2 cup shredded cheese.

Cover with foil and bake for 30 minutes. Then uncover and bake for 15-20 minutes until cheese is bubbling. Let it sit for 5-10 minutes before serving.